"Killer Character" of Yeast. Genetic analysis of chromosomal and plasmid mutations affecting the killer will continue. Analysis of the double-stranded RNA present in various mutants is also expected to add important information to that already obtained. DNA Replication in Yeast. Mutants defective in ribonuclease H, an enzyme active only on the RNA of DNA-RNA hybrids, are being sought. Such mutants should shed light on the role of this enzyme in DNA replication and other processes.